Torque wrench

ABSTRACT

Preset type torque wrench capable of tightening a screw at a predetermined torque set therein. The wrench has a head rod secured to the torque applying head and a slide rod arranged in parallel to the head rod. A pair of toggle links are provided adjacent to the opposite ends of the slide rod and each pivotally connected to the head rod and the slide rod. A compression spring is interposed between the head rod and the slide rod so as to urge the head rod and the slide rod in the opposite directions lengthwise thereof.

United States Patent [191 Tsu'i [111 3,869,941 Mar. 11,1975

TORQUE WRENCH [75] Inventor: Hiroshi Tsuji, Tokyo, Japan [73] Assignee:Tonichi Manufacturing Co., Ltd.,

Tokyo, Japan [22] Filed: May 22, 1974 [21] Appl. No.: 472,369

[30] Foreign Application Priority Data Aug. 29, 1973 Japan 48-97029 [52]US. Cl. 81/52.5 [51] Int. Cl. B25b [58] Field of Search 8l/52.4 R, 52.5

[56] References Cited UNITED STATES PATENTS 2,268,081 12/1941 Pagnard8l/52.5

Primary Examiner-James L. Jones, Jr. Attorney, Agent, or Firm-Totem,McGeady and Stanger [57] ABSTRACT Preset type torque wrench capable oftightening a screw at a predetermined torque set therein. The wrench hasa head rod secured to the torque applying head and a slide rod arrangedin parallel to the head rod. A pair of toggle links are providedadjacent to the opposite ends of the slide rod and each pivotallyconnected to the head rod and the slide rod. A compression spring isinterposed between the head rod and the slide rod so as to urge the headrod and the slide rod in the opposite directions lengthwise thereof.

3 Claims, 6 Drawing Figures Keen 81/524 R minimum I ma 3. 869,941

SHEET 1 95 2 F/G.2 F/G.3

BACKGROUND OF THE INVENTION The present invention relates toimprovements in a preset type torque wrench capable of tightening ascrew at a predetermined torque manually or by a driving motor.

A preset type torque wrench as described above is provided therein amechanism generating a sound or a tactile impression when the tighteningreaches a predetermined torque so that the operator is aware of thecompletion oftightening by the sound or the tactile impression. Varioustypes have been utilized for this mechanism. One of the mostconventional types of this mechanism is that in which a toggle linkmechanism is used.

However, in the prior art torque wrench using the toggle link mechanismhas a disadvantage in that the actual torque for tightening the screwvaries from the set torque when the point at which the force is appliedto the torque wrench varies. In effect, it is difficult to maintain thepoint at which the force is applied to the wrench at a fixed position,thereby rendering the accuracy in the torque for tightening the screw tobe deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a preset type torque wrench using a toggle link mechanism inwhich the actual torque for tightening the screw is kept constantregardless of the fact that the point at which the force is applied tothe torque wrench varies.

The other object is to provide a preset type torque wrench of the typedescribed above in which the mechanism for presetting the torque isarranged within the handle of the torque wrench to which the force isapplied.

The above objects are achieved in accordance with the present inventionby the provision of a torque wrench having a head rod secured to thetorque applying head of the wrench, a slide rod arranged in parallel tothe head rod, a pair of toggle links arranged adjacent to the oppositeends of the slide rod and each pivotally connected to the head rod andthe slide rod, and a spring interposed between the head rod and theslide rod so as to urge the head rod and the slide rod in the oppositedirections lengthwise thereof.

In accordance with a further feature of the present invention, thelength of one of the toggle links is made different from that of theother toggle link while the toggle setting angle between one of thetoggle links and the head rod is made correspondingly different fromthat between the other toggle link and the head rod.

By the above arrangement, the actual torque of the torque wrench fortightening the screw is made constant regardless of the position atwhich the force is applied to the torque wrench.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view, partly incross-section, showing the internal construction of an example of theprior art torque wrench;

FIGS. 2 and 3 are side views showing the general configurations of someexamples of the prior art torque wrench;

FIG, 4 is a fragmentary sectional view, with the torque applying headbeing omitted, showing the main portions of an embodiment of the torquewrench constructed in accordance with the present invention;

FIG. 5 is a fragmentary sectional view similar to FIG. 4 but showing themanner of operation of the torque wrench shown in FIG. 4; and

FIG. 6 is a schematic diagram showing the relationship between variouscomponents of the forces applied to the torque wrench shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Prior to thedescription of the present invention, a brief description of the priorart torque wrench is given below with reference to FIGS. 1 to 3.

In FIG. 1, the torque applying head 1 of the torque wrench is pivotallysupported by a head pin 3 to the tube 2 serving as the handle of thetorque wrench. The inner end of the head 1 is pivotally connected to oneend of the toggle line 5, the opposite end of which is pivotallyconnected to one end of the slide rod 6 having a roller adapted toslidably contact with the inner wall of the tube 2.

The opposite end of the slide rod 6 is attached to a member slidable inthe tube 2 and contacting with one end of a compression spring 4 housedin the tube with the opposite end secured by an adjustable memberadjustably secured to the tube 2 so as to urge the slide rod 6 towardthe head 1 with a force F.

As shown, the toggle link 5 is positioned at an angle a with respect tothe vertical line, so that the roller of the slide rod 6 is slidablyurged against theinner wall of the tube 2 by the force F.

When a force P applied to the tube 2 at a position remote from the'headl is increased, a torque T applied to a screw engaging with the head 1increases, and, when the torque T reaches a limit, the head 1 is swunganticlockwise relative to the tube 2 so that the toggle link 5 isactuated so as to urge the slide rod 6 apart from the head 1 against theforce F applied by the spring 4, thereby giving indication that thetorque T reaches the predetermined value set by the force F of thespring 4.

Assuming that the distance between the center of the screw to which thetorque T is to be applied and the head pin 3 is lh and the distancebetween the head pin 3 and the pivot point of the toggle link 5 to theslide rod 6 is r, while the distance between the center of the screw andthe point at which the force P is applied is l, the torque T isexpressed by the following equations:

T= P lh r.F.cot 01 plied, i.e., the value I, varies, thereby making itdifficult to maintain the torque to be applied to the screw at a desiredconstant value exactly, because it is difficult in the actual practiceto keep the value of l constant.

Although it is possible to lessen the influence by the portion lto whichthe force P is given by shortening the length lh from the center of thebolt to the head pin, the length lh will be considerably large in casewhen the top end of the head is bent as shown in FIG. 2, or in case whenthe head portion includes a power device as shown in FIG. 3, so thatonly small change of the portion I to which the force is given willcause a large change of the working torque T.

The present invention avoids the above described disadvantage of theprior art torque wrench and provides a torque wrench in which the torqueto be applied to the screw is always kept accurately at a desiredpredetermined value regardless of the point at which the force isapplied to the torque wrench and the torque limiting mechanism is housedin the handle of the torque wrench to which the force is applied.

Referring now to FIGS. 4 6 showing the preferred embodiment of thetorque wrench of the present invention, a head member 10 for applying atorque to a screw is fixedly secured to a head rod 11. A slide rod 12 isarranged in parallel to the head rod 11 as shown.

A pair of toggle links 13, 14 are provided adjacent to the opposite endsof the slide rod 12 and each pivotally connected at its opposite ends tothe head rod 11 and slide rod 12, respectively, the links l3, 14 beingoriented obliquely with respect to the length of the head rod 11 asshown.

A compression spring 15 is interposed between the head rod 11 and theslide rod 12 with its one end secured to a portion of the slide rod 12adjacent to the pivot point of the link 13 while the other end of thespring 15 is held by a member, which is mounted on an adjusting screwthreadedly engaged with a portion of the head rod 11 adjacent to thepivot point of the link 14, so that the compressive force of the spring15 is made adjustable by rotating the adjusting screw 20.

A stopper 16 is secured to the head rod 11 as shown, while rollers 19are provided adjacent to the opposite ends of the slide rod 12.

A tube-like cover 17 is swingably connected to a portion of the head rod11 exterior of the cover 17 through a connecting link 18 as shown, andthe remaining portion of the head rod 11, the slide rod 12 and thespring 15 as well as'the links 13, 14 are housed in the cover 17. Thus,the stopper 16 of the head rod 11 abuts against the inner wall of thecover 17 at one side thereof while the rollers 19 are urged to slidablycontact with the inner wall of the cover 17 at its opposite side alongthe generating line of the inner wall of the cover 17 by virtue of theaction of the spring 15 and the oblique orientation of the links 13, 14.

Considering the actuation of the torque wrench described above, when aforce P is applied to a point on the cover 17, the head rod 11 is movedrelative to the cover 17 against the action of spring 15 in thedirection opposite to the direction in which the force P is applied.Thus, the slide rod 12 swingably connected to the head rod 11 throughthe toggle links 13, 14 is moved along the inner wall of the cover 17 tothe right in FIG. 5 relative to the head rod 11 so that the head rod 11abuts against the slide rod 12 as shown in FIG. 5, thereby givingindication that a predetermined value of the torque is reached.

In other words, the force P is applied to the slide rod 12 during theoperation and, when the torque T reaches a predetermined value, thetoggle links 13, 14 are actuated so as to engage the head rod 11 withthe slide rod 12 against the force F of the spring 15 the value of whichis adjustable.

It is now assumed that:

P, Vertical component of the force applied to the toggle link 13.

P Vertical component of the force applied to the toggle link 14.

F, Horizontal reaction force of the toggle link 13.

F Horizontal reaction force of the toggle link 14.

L Distance between the center of the screw to be tightened and the pivotpoint of the toggle link 13 to the slide rod 12.

l= Distance between the pivot point of the toggle link 13 to the sliderod 12 and the pivot point of the toggle link 14 to the slide rod 12.

l, Distance between the pivot point of the toggle link 13 to the sliderod 12 and the point at which the force P is applied.

1 Distance between the point at which the force P is applied and thepivot point of the toggle link 14 to the slide rod 12.

a, Angle formed between the toggle link 13 and the longitudinal axis ofthe head rod 11.

a Angle formed between the toggle link 14 and extension of thelongitudinal axis of the head rod 11. Then, the torque T is expressed asfollows:

T= P-(L 1,)

P, P-l /l P P-l,/l

F, P, cot a,

F2 P2 a F F, F PH (1 cot a, +1, cot a From equation (4) l(L+l,)F

l cot a +l cot 12 cot a Cot 01 Then, the equation (10) is rewritten asfollows:

T L-F/cot 01,

Therefore, it is apparent that, when the angles a 01 are selected tosatisfy the equation (1 l then the torque T applied to the screw willnot vary even though the position at which the force P is applied, i.e.,the values l l varies.

Further, as seen from FIGS. 4 and 5, when the lengths of the togglelinks 13, 14 are selected to be different from each other, the angle oris generally greater than the angle :1 with the length a of the togglelever 13 being smaller than the length a of the toggle link 14, and thehead rod 11 is moved substantially in the translational movementparallel to the slide rod 12 (FIG. 5), thereby affording convenienttactile impression while the spring is conveniently arranged between therods 11, 12.

Referring to FIG. 6, deviation in the torque T might occur, when theforce P is applied obliquely as the force P with an angle 0 formedbetween the perpendicular to the cover 17 and the direction of the forceP, because a horizontal component P-sin 6 of the force P directlyaffects the force F of the spring 15.

In order to avoid the above error, the slide rod 12 is provided withrollers 19 freely slidable along the inner wall of the cover 17. Thus,when the force P is applied to the cover 17, the head rod 11 is moved tourge the slide rod 12 along the inner wall of the cover 17 by the freerolling of the rollers 19 of the slide rod 12 thereby permitting onlythe vertical component of the force P to be transmitted to the torquewrench even though the force P is applied in the direction obliquely ofthe perpendicular to the cover 17 without causing any deviation in thetorque T.

As described above, the position at which the force is applied to thetorque wrench for tightening the screw can be selected at any positionin the wide range of the handle cover without causing any errors in thetorque to be applied to the screw, thereby permitting accuratetightening effect to the obtained.

1 claim:

1. Preset type torque wrench having a toggle mechanism therein, whereinthe improvement comprises a head rod secured to the torque applying headof said wrench, a slide rod arranged in parallel to said head rod, twopairs of toggle links arranged in spaced relationship from each otherlengthwise of said head rod and said slide rod adjacent to the oppositeends of said slide rod and each pivotally connected to said head rod andsaid slide rod, and a spring interposed between said head rod and saidslide rod and connected thereto.

2. Torque wrench according to claim 1, wherein the length of one of saidtoggle links forming said pair is set to be different from that of theother of said toggle links while the toggle setting angle formed betweensaid one of said toggle links and said head rod as well as said sliderod is set to be correspondingly different from that formed between saidother of said toggle links and said head rod as well as said slide rod.

3. Torque wrench according to claim 1, wherein said slide rod isarranged within a tubular handle slidably along the generating line ofsaid handle.

1. Preset type torque wrench having a toggle mechanism therein, whereinthe improvement comprises a head rod secured to the torque applying headof said wrench, a slide rod arranged in parallel to said head rod, twopairs of toggle links arranged in spaced relationship from each otherlengthwise of said head rod and said slide rod adjacent to the oppositeends of said slide rod and each pivotally connected to said head rod andsaid slide rod, and a spring interposed between said head rod and saidslide rod and connected thereto.
 1. Preset type torque wrench having atoggle mechanism therein, wherein the improvement comprises a head rodsecured to the torque applying head of said wrench, a slide rod arrangedin parallel to said head rod, two pairs of toggle links arranged inspaced relationship from each other lengthwise of said head rod and saidslide rod adjacent to the opposite ends of said slide rod and eachpivotally connected to said head rod and said slide rod, and a springinterposed between said head rod and said slide rod and connectedthereto.
 2. Torque wrench according to claim 1, wherein the length ofone of said toggle links forming said pair is set to be different fromthat of the other of said toggle links while the toggle setting angleformed between said one of said toggle links and said head rod as wellas said slide rod is set to be correspondingly different from thatformed between said other of said toggle links and said head rod as wellas said slide rod.